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Remarks on W. Truran's article “on Errors committed by writers on Mechanical Engineering”
304
Civil
Engineering.
6. With regard to the trepidations of the screw. That when the pro. pelting surface is arranged in one blade, the trepidations are very strcmg; when arranged in two blades, light; when arranged in three blades, nearly insensible, and when in four blades they entirely ceased. '7. With regard to the influence exerted on the slip by the greater or less rotary speed of the same screw. That the slip of the same screw remained constant at all rotary velocities, the speed of the boat being in the direct ratio of the number of revolutions m,~de by the screw in a given time. 8. With regard to the influence exerted on the slip by surroundb~g the Teriphery of the screw with a thin metallic drum of the same length as the screw,fastened to the blades and turning with them. That the application of such a drum produees no effeet on the slip. 9. lVith regard to the in/luence exerted on the slip by arranging the blctdes checkerwise. That the arrangement of the blades cheekerwise, which is done by taking half the number of the blades, moving them back fl~eir length, and positioning them so that the rear blades intersect the spaces between the front blades, which arrangement causes the screw to be of double length in the direction of the axis, exerts no influence on the slip of the screW. 10. grit+ rezard to the iT~ue7~ce exerted on the slip by the length of the fitch. That the slips of otherwise equal screws are in the direct ratio of the pitches ; that is to say, doubling the pitch doubles the slip. 11. With regard to the i~fiuenee exerted ou the sllp by the length of the diameter O/'lhe screw. That the slips of otherwise equal screws are in tl~e ratio of the squares of the diameters ; that is to say, halving the diameter increases the slip four times. (To be Continued.) For the Journal of the Franklin Institute. Remark~ on W. TRvaA~'s ./Trtiele " on Errors committed by Wrifers on .Mechanical Engineering." By THomAs Pttoss~a, Cir. Eng. In the March number of the Journal, is an article on "Nrrors committed by writers on .Mechanical Engineering," by WILLIA~ 'Fau~A~, Esq., which is certainly astonishing, not tbr tile errors which it exposes, but tbr those which it commits. The quoted assertion of Desaga]iers, that" two men working at a windlass with handles at right angles to each other, can raise 701bs. more easily than one can raise 30 lbs.~" has reference only to their physical organization, which is supposed to enable them to work with greater advantage when one man is laboring most and the other least, and thus equalizing the labor or strain at certain points, which otherwise would test the strength too severely to be endured ; just as a man may in some eases perhaps, lift or carry 60 lbs. 70 feet with greater ease than 70 lbs. 60 feet, although the mere mechanical performances are precisely equal. That "the majority of educated scientific men in Europe believe that a gain of power tbtlows, when the handles of a windlass are set at right angles &e.," is a most extraordinary assertion of credulity on the part of the writer.
On Errors in Writers on 2t~ec]~anlcalEngineering.
305
The ~ratuitous addition of C. E. to the name of the late J, C. Robertson, Esq., is very slgmficant of the writer s accuracy, and would certainly amuse the rempient, were he alive to enjoy the joke. Mr. Robertson was a writer to the Signet in Scotland. In 1823 he commenced the editorship of the London .Mechanics' .lLlagazine,* and]fi 1835 he connected with it a Patent Agency business. He died Sept. '25th, 1852, and this is, I believe, the first obituary notice that has ever appeared in any Scie~zt~c .In,tribal, of the man, who, before the London Mechanics' Institute was established, advocated and encouraged the claims of mechanics, and identihed himself with that Institute from its commencement-the man who received the highest encomiums from Dr. Birkbeck and Henry Brougham, Esq., M. P. and F. R. S., himself the most accomplished mechanic that ever argued a Patent Case in a silk gown, or sat upon a woolsack~now Lord Brougham.]" Desaguliers alludes to the " easily" doing of a thing, not to the power required Lo do it. One may do a thing, which another cannot do at all, or the same man do a thing one way which he cannot do another, while the absolute mechanical power which is required to do it remain8 precisely the same. The quotation from . Robcrtson . I. cannot .find, but. the language is very indetinite and quite unlike that winch he usually employed m writing upon subjects which he understood, ~hich were certainly not those al, luded to ; at least, he was not so eminent as has been stated, apparently in order to make out a ease. The placing of cranks at right angles to each other, was, I believe~ first introduced by Bohon & Watt, nearly 50 years ago, in a rolling mill. The object in ~'iew, was, to avoid the dead eentres which exist when one engine only is employed, and also to use a lighter fly-wheel to equalize the motion, a most important consideration too m a cotton mill, particularly where very fine numbers are spun. The first steamboat with two engines, was upon the Clyde, in ]813, built also by Boltoa & Watt, and had the cranks placed at right angles to each other. It is only on a loeomoti~,e, that 1 fancy any power is gained by placing the cranks at right angles to each uther, and that is the power of throwing the engine off the rails, particularly when well "backed up '~ by a considerable elevation of the outer rail on going round a curve. One engine pulls on one side~ and then the other reciprocates it at inter° vals on the other side, which, being favored by the elevation of the outer rail upon a curve, sets the engine and train rocking until it not unfrequently rocks itself off. Mr. Stephenson took some such view of the v
.
.
o
~
•
~,::
" I n the first Vol., he noticed in his Report of the proceedings for the establis'hmerit of the London Mechanics ~ Institute,of which he was one of the Secretaries, that one of the speaker's mode of pronouncing some words, excited a smile, and his friends must have smiled on reading it, for his own pronunciation was, tbr an educated man, the brbadest of Scotch, and so continued until the davy of his death, lie was of a kindly and social disposition, but a hard worker withal. "{'The man who originated ahnost, the London Mechanics' Institute, and who had therefore, if tbr nothing else, a right to say that " he had done the State Some service," and who died in its "harness," received not one passing notice from the press, on his demise, and even the offspring which he had raised with so much anxiety and solicitude, shed not the tribute of a tear of printers' ink upon its pages, to announce to the world that its progenitor had departed this life at the age of 67. 'aft*
306
Oivfl ~ngineen*r~g.
matter ~hen he invented his three cylinder locomotives, which, notwith+ ~tanding his high reputatioo, the necessity ~0r ~s scarcely ~s yet ~eknow. !edged+ And, theretbre, I do not expect too m3k?f:onverts to ,+hepropo. sition which I advanced several ) ears ~g Z o r the doin~ of which I l~ave only obtained the abuse of those who assume to be the elite of railway engineering +NeW York~ Jlpril 2, 1855, F,,*r the 3+~m+~'+Iof flxe Fra~klin Institute+
Investigation of the o%g&+Btodc of tlowe's 2~'uss+ By & M. R~e~am~so~r+
A point of great prac6cal i:mportance in construetior~ ~s~ that all l~e parts ++botddfit ; so that+ when put together, they may constitute a perfect whole. Under-plnning, or x~e~lging and ke) ing~ to remedy any deficiency of length, breadth, or thickness of the components, is ia the highest de+ ~ree d~leterious, and atway~ endangers the stability of the stmetur~ '~'~ dimenmons, therefore, of each part should be accurately determined be. forehand, and no one should be received which does not eorrespond~ ia every particular, with the conditions previous|y ascertained. With the view of contributing my mite towards perfecting the de+ai~s of bridge eonstrtmfio% I submit the following general investigation of the angle-block of Howe's Truss, the diagonal brace being perpe]~dieulat to
+
r
+ +
.... +,
+~
2 _ _ _ ~
+
LetA B C D b e a p a n e l of Howe~s truss A B - - ~ , t ; A C i d ~r; A d== ~ , ¢ d --half d~stance between abutting surfaces of block--ei eg=c; ef=x;fg=+~ ac
d ,~2d
From
efg,
+~j.~.b+p;
ae~ d~,2e~x~a~x.
The right triangles, a e c ~nd e f g , are simi[ae ~+ ef : j~ g : : a c : a e, or x + ~, : • ~ , :: , and ~,tve the prvportion, ~
~' ~," "t- y .
.
-
(t)
-
.
(21
Civil
Engineering.
6. With regard to the trepidations of the screw. That when the pro. pelting surface is arranged in one blade, the trepidations are very strcmg; when arranged in two blades, light; when arranged in three blades, nearly insensible, and when in four blades they entirely ceased. '7. With regard to the influence exerted on the slip by the greater or less rotary speed of the same screw. That the slip of the same screw remained constant at all rotary velocities, the speed of the boat being in the direct ratio of the number of revolutions m,~de by the screw in a given time. 8. With regard to the influence exerted on the slip by surroundb~g the Teriphery of the screw with a thin metallic drum of the same length as the screw,fastened to the blades and turning with them. That the application of such a drum produees no effeet on the slip. 9. lVith regard to the in/luence exerted on the slip by arranging the blctdes checkerwise. That the arrangement of the blades cheekerwise, which is done by taking half the number of the blades, moving them back fl~eir length, and positioning them so that the rear blades intersect the spaces between the front blades, which arrangement causes the screw to be of double length in the direction of the axis, exerts no influence on the slip of the screW. 10. grit+ rezard to the iT~ue7~ce exerted on the slip by the length of the fitch. That the slips of otherwise equal screws are in the direct ratio of the pitches ; that is to say, doubling the pitch doubles the slip. 11. With regard to the i~fiuenee exerted ou the sllp by the length of the diameter O/'lhe screw. That the slips of otherwise equal screws are in tl~e ratio of the squares of the diameters ; that is to say, halving the diameter increases the slip four times. (To be Continued.) For the Journal of the Franklin Institute. Remark~ on W. TRvaA~'s ./Trtiele " on Errors committed by Wrifers on .Mechanical Engineering." By THomAs Pttoss~a, Cir. Eng. In the March number of the Journal, is an article on "Nrrors committed by writers on .Mechanical Engineering," by WILLIA~ 'Fau~A~, Esq., which is certainly astonishing, not tbr tile errors which it exposes, but tbr those which it commits. The quoted assertion of Desaga]iers, that" two men working at a windlass with handles at right angles to each other, can raise 701bs. more easily than one can raise 30 lbs.~" has reference only to their physical organization, which is supposed to enable them to work with greater advantage when one man is laboring most and the other least, and thus equalizing the labor or strain at certain points, which otherwise would test the strength too severely to be endured ; just as a man may in some eases perhaps, lift or carry 60 lbs. 70 feet with greater ease than 70 lbs. 60 feet, although the mere mechanical performances are precisely equal. That "the majority of educated scientific men in Europe believe that a gain of power tbtlows, when the handles of a windlass are set at right angles &e.," is a most extraordinary assertion of credulity on the part of the writer.
On Errors in Writers on 2t~ec]~anlcalEngineering.
305
The ~ratuitous addition of C. E. to the name of the late J, C. Robertson, Esq., is very slgmficant of the writer s accuracy, and would certainly amuse the rempient, were he alive to enjoy the joke. Mr. Robertson was a writer to the Signet in Scotland. In 1823 he commenced the editorship of the London .Mechanics' .lLlagazine,* and]fi 1835 he connected with it a Patent Agency business. He died Sept. '25th, 1852, and this is, I believe, the first obituary notice that has ever appeared in any Scie~zt~c .In,tribal, of the man, who, before the London Mechanics' Institute was established, advocated and encouraged the claims of mechanics, and identihed himself with that Institute from its commencement-the man who received the highest encomiums from Dr. Birkbeck and Henry Brougham, Esq., M. P. and F. R. S., himself the most accomplished mechanic that ever argued a Patent Case in a silk gown, or sat upon a woolsack~now Lord Brougham.]" Desaguliers alludes to the " easily" doing of a thing, not to the power required Lo do it. One may do a thing, which another cannot do at all, or the same man do a thing one way which he cannot do another, while the absolute mechanical power which is required to do it remain8 precisely the same. The quotation from . Robcrtson . I. cannot .find, but. the language is very indetinite and quite unlike that winch he usually employed m writing upon subjects which he understood, ~hich were certainly not those al, luded to ; at least, he was not so eminent as has been stated, apparently in order to make out a ease. The placing of cranks at right angles to each other, was, I believe~ first introduced by Bohon & Watt, nearly 50 years ago, in a rolling mill. The object in ~'iew, was, to avoid the dead eentres which exist when one engine only is employed, and also to use a lighter fly-wheel to equalize the motion, a most important consideration too m a cotton mill, particularly where very fine numbers are spun. The first steamboat with two engines, was upon the Clyde, in ]813, built also by Boltoa & Watt, and had the cranks placed at right angles to each other. It is only on a loeomoti~,e, that 1 fancy any power is gained by placing the cranks at right angles to each uther, and that is the power of throwing the engine off the rails, particularly when well "backed up '~ by a considerable elevation of the outer rail on going round a curve. One engine pulls on one side~ and then the other reciprocates it at inter° vals on the other side, which, being favored by the elevation of the outer rail upon a curve, sets the engine and train rocking until it not unfrequently rocks itself off. Mr. Stephenson took some such view of the v
.
.
o
~
•
~,::
" I n the first Vol., he noticed in his Report of the proceedings for the establis'hmerit of the London Mechanics ~ Institute,of which he was one of the Secretaries, that one of the speaker's mode of pronouncing some words, excited a smile, and his friends must have smiled on reading it, for his own pronunciation was, tbr an educated man, the brbadest of Scotch, and so continued until the davy of his death, lie was of a kindly and social disposition, but a hard worker withal. "{'The man who originated ahnost, the London Mechanics' Institute, and who had therefore, if tbr nothing else, a right to say that " he had done the State Some service," and who died in its "harness," received not one passing notice from the press, on his demise, and even the offspring which he had raised with so much anxiety and solicitude, shed not the tribute of a tear of printers' ink upon its pages, to announce to the world that its progenitor had departed this life at the age of 67. 'aft*
306
Oivfl ~ngineen*r~g.
matter ~hen he invented his three cylinder locomotives, which, notwith+ ~tanding his high reputatioo, the necessity ~0r ~s scarcely ~s yet ~eknow. !edged+ And, theretbre, I do not expect too m3k?f:onverts to ,+hepropo. sition which I advanced several ) ears ~g Z o r the doin~ of which I l~ave only obtained the abuse of those who assume to be the elite of railway engineering +NeW York~ Jlpril 2, 1855, F,,*r the 3+~m+~'+Iof flxe Fra~klin Institute+
Investigation of the o%g&+Btodc of tlowe's 2~'uss+ By & M. R~e~am~so~r+
A point of great prac6cal i:mportance in construetior~ ~s~ that all l~e parts ++botddfit ; so that+ when put together, they may constitute a perfect whole. Under-plnning, or x~e~lging and ke) ing~ to remedy any deficiency of length, breadth, or thickness of the components, is ia the highest de+ ~ree d~leterious, and atway~ endangers the stability of the stmetur~ '~'~ dimenmons, therefore, of each part should be accurately determined be. forehand, and no one should be received which does not eorrespond~ ia every particular, with the conditions previous|y ascertained. With the view of contributing my mite towards perfecting the de+ai~s of bridge eonstrtmfio% I submit the following general investigation of the angle-block of Howe's Truss, the diagonal brace being perpe]~dieulat to
+
r
+ +
.... +,
+~
2 _ _ _ ~
+
LetA B C D b e a p a n e l of Howe~s truss A B - - ~ , t ; A C i d ~r; A d== ~ , ¢ d --half d~stance between abutting surfaces of block--ei eg=c; ef=x;fg=+~ ac
d ,~2d
From
efg,
+~j.~.b+p;
ae~ d~,2e~x~a~x.
The right triangles, a e c ~nd e f g , are simi[ae ~+ ef : j~ g : : a c : a e, or x + ~, : • ~ , :: , and ~,tve the prvportion, ~
~' ~," "t- y .
.
-
(t)
-
.
(21